Twelve lead ECG measurements are often used to analyze a patient's heart condition, and physicians are trained to interpret such measurements. In a clinical setting, the measurements are generated by attaching electrodes to the patient's hands, feet, and six locations on the patient's chest. Each chest measurement is made by measuring the potential as a function of time between one of the chest leads and the average of the potentials between the hands and one of the feet. This average is often referred to as “Wilson's Central-terminal”. Unfortunately, generating such measurements in the field when the patient experiences symptoms that might correspond to a heart attack or other cardiovascular problem presents problems, since the conventional equipment and technicians are not usually available to connect the patient to the ECG device and make the measurements.
A number of portable ECG devices have been proposed to overcome the problem of making ECG measurements in the field. When a patient determines that the patient might be having a cardiac event, the patient uses the device to measure one or more ECG traces. If the device detects an anomaly in the traces, the results are sent to a physician for interpretation.
For example, U.S. Pat. No. 8,082,025 describes a handheld ECG device that measures the chest traces by placing the device against the corresponding locations of the patient's chest while holding the device in the patient's hands. The device is held such that one hand electrode on the device is in contact with the patient's left hand, and another hand electrode on the device is in contact with the patient's right hand. A chest measurement is then generated by measuring the potential between a third electrode that is in contact with the patient's chest and the average of the potentials measured by the hand electrodes. While the resultant ECG traces are a good approximation to the conventional chest traces, these traces can differ significantly from the conventional traces, and hence, present interpretation problems for physicians who are trained to interpret conventional ECG traces.
While an additional electrode could be attached between the device and the patient's foot or upper thigh to provide traces that more closely approximate the conventional ECG chest traces, the addition of such an electrode presents other problems. First, the electrode must be incorporated in the device in a manner that allows the electrode to be deployed and attached to the patient's leg by a wire. The wire and attachment mechanism are bulky, and hence, not easily incorporated in the device. If the wire and attached electrode are separate from the device, the electrode assembly is easily lost. The conventional attachment mechanisms utilize adhesively attached electrodes. These electrodes are not suitable for repeated use by a patient in the field; hence, some form of attachment that requires a band that holds the leg electrode against the patient's body is needed. This further increases the bulk of the portable device. In addition, the patient must be capable of attaching the electrode to the correct location. In the case of an elderly patient or someone with limited flexibility, attaching the leg electrode presents additional challenges.